The field of the disclosure relates generally to satellite service transmission systems, and particularly to management of fixed satellite service protection using real-time measurements.
Conventional fixed satellite service (FSS) earth stations, or sites, operate across a variety of spectrum bands for Geostationary Earth Orbit (GEO) satellites. The citizens band radio service (CBRS), defined by the FCC for fixed wireless and mobile communications operates in the 3550-3700 MHz (3.55-3.7 GHz) band and use of this spectrum is authorized and managed by a Spectrum Access System (SAS). The function of the SAS is to maintain a database of all transmitters that use the CBRS band, including the transmitter locations and transmitter powers. The SAS uses a propagation model to determine interference between each FSS site and radio access points (AP) to ensure globally across the totality of its management area that the interference is below an acceptable interference threshold at each location. The SAS uses frequency planning algorithms known in the field of cellular communications for Frequency Division Multiple Access (FDMA), such as GSM. Thus, the SAS is able to allocate to each AP or citizens broadband radio service device (CBSD), the frequency of operation, bandwidth, and transmitter power.
The C-band, which is designated by the IEEE and used for satellite communications, covers the 3-8 GHz band. The FSS incumbents in the 3.7-4.2 GHz of downlink C-band are identical in nature and technology to the FSS incumbents within the 3.55-3.7 GHz CBRS band, and these incumbents are provided co-channel and adjacent-channel protection (out of band) under the Part 96 rules of the United States Federal Communications Commission (FCC). FSS incumbents within the CBRS band use 3.665 to 3.7 GHz. Additionally, there is a requirement to limit the amount of aggregate interference across the entire downlink band to avoid gain compression at the Low Noise Amplifier (LNA) used for satellite signal reception. The CBRS band is considered fairly manageable at present due to the relatively small number of FSS sites (<100). In contrast, the 3.7-4.2 GHz band presently includes over 4700 registered FSS sites, and may include as many or more unregistered FSS sites.
There are approximately, at this time, 160 geostationary satellites utilizing the C-band for downlink in the 3.7-4.2 MHz spectrum. Each satellite typically employs 24 transponders, each with a 36 MHz signal bandwidth. Carrier spacing is 40 MHz, 2×500 MHz used on each satellite, and 12 carriers each for horizontal and vertical polarization. The carrier-to-noise (C/N) margins are typically 2-4 dB. The earth stations typically employ multiple satellite dishes and frequency agile receivers to decode specific video/data streams off individual transponders. The actual received bandwidth at the FSS sites varies. Multiple dish antennas are often used to obtain programming from multiple satellites. The United States C-band frequency chart is shown below (in GHz) in Table 1.
TABLE 1(Frequencies in GHz)HorizontalHorizontalVerticalVerticalUplinkDownlinkChannelDownlinkUplink3.72015.9455.96523.7403.76035.9856.00543.7803.80056.0256.04563.8203.84076.0656.08583.8603.88096.1056.125103.9003.920116.1456.165123.9403.960136.1856.205143.9804.000156.2256.245164.0204.040176.2656.285184.0604.080196.3056.325204.1004.120216.3456.365224.1404.160236.3856.405244.180
The C-band downlink spectrum includes 500 MHz adjacent to the CBRS band, but sharing this adjacent spectrum with mobile and fixed wireless usage has been problematic for technological reasons, and according to the existing protection rules, which are highly conservative in nature. Satellite receivers, for example, are extremely sensitive, having an interference threshold of −129 dBm/MHz according to the requirement from FCC Part 96, and operate below the thermal noise level of the actual band itself, often working with effective thermal noise of 80K, with high gain antennas (satellite dishes) to amplify a weak satellite signal before detection. Relatively small power transmitters sharing the same band may cause interference over distances of tens of kilometers or greater.
There is no system currently in place to monitor and report operating parameters, such as the actual frequency channel usage or the direction and elevation of reception of the satellite dish with its dish size (which determines its gain for satellite reception) at each FSS site. Accordingly, the protection rules are conservative because existing SAS schemes have no capability to remedy FSS interference. Furthermore, no conventional propagation models accurately predict the transmission loss between the transmitter and the receiver, or to the FSS site from the point of interference, which further encourages over protection of FSS sites from wireless transmitters that occupy the same band. Additionally, building construction/demolition, as well atmospheric effects, including change from one season to another, can cause unpredictable propagation behavior, and FSS site operators may frequently change the FSS site operating parameters, which encourages the operators to register their respective FSS sites for full arc and full bandwidth protection when, in practice, the actual use may be much more restricted.
FIG. 1 is a schematic illustration of a conventional satellite service protection scheme 100 for an FSS site 102. FSS site 102 includes at least one earth satellite ground station 104, or earth station 104, which generally includes a dish and a frequency agile receiver (not separately numbered), for receiving and decoding video/data streams from satellite 106 (e.g., GEO C-band satellite). Protection scheme 100 further includes a CBSD 108, which may be a base station in the cellular context, such as an eNodeB for LTE, mounted on a vertical support or tower 110. CBSD 108 may be a radio access point (AP) used for fixed wireless access. Authorization and resource allocation of CBSD 108 is governed by an SAS 112, which is in operable communication with CBSD 108 over a data link 114 (e.g., wireless or wired Internet connection, etc.).
In operation of protection scheme 100, CBSD 108 requests authorization and resource allocation from SAS 112. SAS 112 has knowledge of the operating parameters of FSS site 102, which are communicated over a reporting link 115. Initially, the resource allocation to CBSD 108 can be provided using a propagation model to avoid interference. This interference modeling can model co-channel, adjacent channel, second adjacent channel, and aggregate band interference. In this example, SAS 112 may use a frequency planning algorithm that is similar to a model used for cellular networks to determine the allocation of both the channel frequency and power. However, this modeling technique is not aware of the actual loss between CBSD 108 and FSS site 102, which may influenced by obstructions 116 (buildings, elevated ground, seasonal effects, foliage, etc.) along an actual transmission path 118 therebetween. SAS 112 therefore implements protection scheme 100 according to an estimate model that utilizes a mapped distance 120 between CBSD 108 and FSS site 102 to predict a pass loss estimate.
However, because SAS 112 cannot measure the actual loss along the actual transmission path 118, the path loss estimate will be inaccurate, and typically based on the worst-case scenario. Such inaccuracies therefore generally encourage over protection of the FSS sites and results in limited CBRS spectrum utilization, as well as the C-band downlink spectrum overall. Accordingly, it would be desirable to develop an FSS protection scheme that can determine actual path loss considerations in real time to maximize use of available spectra, but without impairing the protection to the sensitive satellite receivers.
FIG. 2 is a schematic illustration of a conventional satellite service protection system 200 implementing protection scheme 100, FIG. 1, for earth station 104 receiving a video/data stream 202 from satellite 106. In this example, stream 202 has a total transmit spectrum of 500 MHz between 3700 MHz and 4200 MHz, that is, 500 MHz of the GEO C-band satellite downlink spectrum adjacent to the CBRS band. Under the current government rules, protection scheme 100 implements the FCC Part 96 protection scheme for 3600-3700 MHz earth stations. System 200 includes a low-noise block (LNB) 204 and a headend 206. LNB 204 includes, for example, a feed horn 208, a bandpass filter 210, and an LNA/downconverter 212. An FCC reference point (not shown), for interference calculations by the SAS, is generally taken between bandpass filter 210 and LNA 212. Headend 206 includes a plurality of channel receivers 214.
In operation of system 200, LNB 204 functions as the receiving device for the dish of earth station 104, collecting from the dish the amplified received radio waves as a block of frequency sub-blocks a through 1 (e.g., 12×40 MHz channels, see Table 1, above). LNB 204 amplifies and downconverts the collected block into a lower block of intermediate frequencies (IF) (e.g., 950-1450 MHz), which are then distributed as individual sub-blocks (c, f, b, i in this example) along a receiver signal distribution chain 216 to respective channel receivers 214, which are typically contained in a distribution rack in headend 206.
In this example, earth station 104 utilizes a 2-meter antenna, with protection of FSS LNB from gain compression of −60 dBm aggregate LNB input signal level from all terrestrial radio emissions within 40 km radius of the FSS across the 500 MHz band. Protection of FSS receiver noise floor is −129 dBm/MHz, as discussed above, from all co-channel terrestrial radio signals within 150 km radius of the FSS, based on maximum noise equal to −10 dB I/N, for 0.25 dB max noise rise at measurement point. It should be noted, that since many FSS sites use the 3.7-4.2 GHz band across the United States, such protection areas of 40 km and 150 km radius frequently overlap each other, and thus the protection criteria to address interference for each radio access point sharing this band must be satisfied at each FSS site within the vicinity.
FCC rules also specify the acceptable levels of adjacent channel interference in the first and second adjacent channels, e.g., which allow 40 and 52 dB higher signal strengths, respectively, for the first and second adjacent channels due to their increased frequency separation from the central channel, to that used for signal reception. Accordingly, the re-use of unused channels is optimally based initially upon the second adjacent channel before the first adjacent channel in an optimization strategy for optimum interference management. The FCC Rules also specify standard FSS dish gain profile (H and V planes) and also band pass filter attenuation. The antenna pattern (not shown) output from the dish is highly directional, the Half Power Beamwidth (HPBW) is approximately 1.3 degrees, and the antenna gain is 36.5 dBI for a 2 m diameter dish with an efficiency of 65%.
Conventionally, not all of the twelve 40 MHz channels (a through 1) over one polarization (see Table 1, above) are actually demodulated along distribution chain 216 for a given FSS site (e.g., FSS site 102, FIG. 1, having 1-N earth stations 104). In the example illustrated in FIG. 2, only a third of the twelve polarization channels (that is, 24 channels in total, but only twelve for each of the two polarizations), are demodulated at headend 206, with protection scheme 100 requiring co-channel protection of an “unused” portion 218 of the transmit spectrum unavailable for use by other CBSDs 220 (or Radio Access Points (RAPs)) seeking authorization and resource allocation from SAS 112 for FSS site 102. That is, in this example, unused portion 218 represents 320 MHz of available terrestrial spectrum that is wasted and unusable under protection scheme 100. Additionally, in consideration of other FSS sites in the vicinity of a particular CBSD/RAP 220 that may utilize different satellite down-link channels, there will be further constraints on the spectrum availability. In areas of high FSS site density, the whole of the 500 MHz of spectrum will become unavailable to the particular RAP.
FIGS. 3A-3B illustrate data tables 300, 302 for loss and separation distances according to the conventional protection scheme 100, FIG. 1, and system 200, FIG. 2. Tables 300 and 302 are each illustrated with respect to co-channel, LNB blocking, first adjacent out-of-band emission (OOBE) and second adjacent OOBE for a single interfering transmitter. In consideration of the loss values taken from table 300, minimum separation distances to reduce interference below the various thresholds in table 302 are determined using a free space path loss (FSL) equation and two common propagations models used for cellular communications: Cost 231 Hata (231 Hata), Cost 231 Walfish-Ikegami (231 WI). These tables illustrate the significant variations in associated protection distances depending on the model choice. For example, for an Azimuth of 0 degrees, a satellite dish elevation of 5 degrees and a satellite gain of 14.5 dB, the predicted separation distance is 6940 km for FSL, 7.4 km for 231 WI and 3.4 km for 231 Hata.
Use of the most conservative model, FSL, will result in massive over protection of the FSS and under-utilization of the spectrum. In the example illustrated, the dish size is 2 m, antenna height of FSS is 4 m, and small cell height is 1.5 m for both 231 WI and 231 Hata. As can be seen from these examples, the FSL calculation is not able to take into account actual terrain/obstacle considerations; the FSL calculation does use assumptions on antenna height. Even the use of other models such as 231 Hata and 231 WL require the choice of parameters that reflect different terrains profiles and even these can produce significant variations within themselves based on that choice. Furthermore, because such empirical models only produce a prediction of the average loss between two points in space, in practice, the actual loss between these two points may significantly depend on many other factors including the terrain therebetween.